In a liquid crystal display device, a TFT substrate over which pixel electrodes and thin film transistors (TFTs), etc. are formed in a matrix shape and a counter substrate over which color filters, etc. are formed at locations corresponding to the pixel electrodes of the TFT substrate in the manner of opposing the TFT substrate are disposed and a liquid crystal is interposed between the TFT substrate and the counter substrate. Then an image is formed by controlling the transmissivity of light in liquid crystal molecules of each pixel.
A liquid crystal display device is widely used in various fields ranging from a large display device such as a TV to a cellular phone, a DSC (Digital Still Camera), etc. since it is flat and lightweight. Meanwhile, a liquid crystal display device has the problem of a view angle characteristic. The view angle characteristic means that brightness varies or chromaticity varies when a screen is viewed from the front and then from an oblique direction. With regard to the view angle characteristic, an In Plane Switching (IPS) method of operating liquid crystal molecules by an electric field in the horizontal direction has an excellent characteristic.
A conventional method of subjecting an alignment film used in a liquid crystal display device to alignment treatment, namely giving alignment control capability, is a method of applying rubbing treatment. The alignment treatment by rubbing is a method of applying alignment treatment by rubbing an alignment film with a cloth. In contrast, there is a method called a photo-alignment method of giving alignment control capability to an alignment film in a noncontact manner. In the IPS method, the performance is better when a pre-tilt angle is small and hence the photo-alignment method is advantageously used.
Meanwhile, in a liquid crystal display device, it is important to control the space between a TFT substrate and a counter electrode. In many cases, the space between a TFT substrate and a counter electrode is controlled by forming a columnar spacer on a counter substrate and forming a plinth to receive the columnar spacer on the TFT substrate. A liquid crystal display device with a touch panel is frequently used in recent years. When a liquid crystal display device is touched, the space between the TFT substrate and the counter substrate of the liquid crystal display panel varies and the positional relationship between a columnar spacer and a plinth deviates. As a result, touching fault such as bleeding or uneven color appears in an image.
A liquid crystal display device having a configuration of setting the positional relationship between a columnar spacer and a plinth so as to be immovable by reducing the area of the plinth smaller than the area of the columnar spacer is described in JP-A No. 2007-164134.
When a columnar spacer is used, an alignment film for initially aligning a liquid crystal is formed also between the columnar spacer and a plinth formed on a TFT. When a liquid crystal display device is touched with a finger or the like, stress is imposed between the columnar spacer and the plinth, giving rise to the phenomenon that the alignment film is shaved and shavings are caused. Such shavings cause the occurrence of blight spots in a display region. Neither such a problem nor a measure is described in JP-A No. 2007-164134.
A photo-alignment film is formed in a double-layered structure in some cases. That is, the upper layer is formed with a material having polyamide acid ester containing cyclobutane and being likely to form photo-alignment by ultraviolet rays as a precursor, and the lower layer is formed with a material having polyamide acid not containing cyclobutane and being mechanically strong as a precursor.
“CF 1” shows the structural formula of polyamide acid ester containing cyclobutane.
(CF 1)

In “CF 1”, Ar represents a divalent aromatic group, R represents an alkyl group having a carbon number of 1 to 8, and each of X1 to X4 represents hydrogen or an alkyl group having a carbon number of 1 to 3 independently.
“CF 2” shows the structural formula of polyamide acid not containing cyclobutane.
(CF 2)

In “CF 2”, Y represents a divalent organic group and Z represents a tetravalent organic group other than cyclobutane.
FIG. 16 is a schematic sectional view of a liquid crystal display device having a double-layered alignment film. In FIG. 16, a passivation film 107 is formed over a TFT substrate 100 including glass. Plural layers including a common electrode are formed between the passivation film 107 and the TFT substrate 100 but are omitted in FIG. 16. Pixel electrodes 108 are formed over the passivation film 107. An alignment film 113 including two layers of a lower alignment film 111 and an upper alignment film 112 is formed in the manner of covering the pixel electrodes 108. The upper alignment film 112 includes a photoreactive material produced by using polyamide acid ester as a precursor, has a film thickness reduced by photoreaction, and has a low mechanical strength. On the other hand, the lower alignment film 111 includes a non-photoreactive material produced by using polyamide acid as a precursor and the film thickness thereof does not reduce even after the irradiation of ultraviolet rays.
In FIG. 16, a black matrix 201 and a color filter 202 are formed over a counter substrate 200. An overcoat film 203 is formed over the black matrix 201 and the color filter 202 but is omitted in FIG. 16. A part where the color filter 202 is formed is a transparent region 400 and an image is formed by light transmitting the transparent region 400. A part where the black matrix 201 is formed is a nontransparent region 500.
In FIG. 16, a columnar spacer 204 to define a space between the TFT substrate 100 and the counter substrate 200 is formed over the black matrix 201. The tip of the columnar spacer 204 touches the upper alignment film 112 over the TFT substrate 100 and a plinth 114 made of the same material as the pixel electrodes 108 is formed at the part. The height of the top end of the plinth is the same as the height of the top ends of the pixel electrodes.
In the upper alignment film 112, photodecomposition reaction is generated by the irradiation of ultraviolet rays, the molecular weight decreases, and the alignment film strength lowers. If a heat shock test of −40° C. to 85° C. for example is applied to such a liquid crystal display device, the upper alignment film 112 peels off at the part of the plinth 114 and a very fine blight spot caused by the shavings is formed. The shavings of the alignment film are formed in the region R surrounded by the dotted line in FIG. 16. That is, it is estimated that a panel warps repeatedly because of the in-plane temperature distribution of the panel caused by a heat shock test, that the columnar spacer 204 formed on the side of the counter substrate 200 shaves the alignment film 113 over the plinth 114 on the side of the TFT substrate 100, that a fraction of the alignment film 113 floats in a liquid crystal, and that hence a blight spot occurs.